Determination of Phosphorus, Germanium, Silicon, and Arsenic

Boltz, D. F.; Mellon, M. G.

doi:10.1021/ac60011a019

Cited by 205 publications

(60 citation statements)

References 27 publications

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“…CoKe radiation was used. Si in solution was determined photometrically by the molybdenum blue method (Boltz and Mellon, 1947) and iron colorimetrically as the o-phenanthroline complex (Asami and Kumada, 1960). For both these determinations an aliquot of the strongly alkaline solution was firstly neutralised.…”

Section: Methodsmentioning

confidence: 99%

The Influence of Silicate on the Transformation of Lepidocrocite to Goethite

Schwertmann¹,

Rm²

1972

Clays and clay miner.

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Abstract--The mechanism of the transformation of lepidocrocite (7FeOOH) to goethite (aFeOOH) has previously been established and the effect of silicate on the transformation was investigated. Rather than completely inhibiting the reaction, as had been suggested, the presence of Si was found to merely retard the nucleation stage of the transformation. There was found to be no decrease in the dissolution rate of the lepidocrocite due to surface adsorption of Si.Si has no effect if introduced after the nucleation stage, and under conditions of pH and temperature where the dissolution rate of the lepidocrocite largely determines the rate of transformation, the presence of Si has a reduced effect. The results show that Si is adsorbed and incorporated into the goethite structure, and due to its retarding effect on the nucleation, larger crystals of goethite are formed, many of which are twinned.It is inferred from the results that the apparent stability of lepidocrocite occurring in soils in association with goethite cannot be attributed solely to the presence of Si in the soil system. INTRODUCTION IN AN earlier paper (Schwertmann and Taylor, 1972) the mechanism and kinetics of the transformation of lepidocrocite (TFeOOH) to its more stable polymorph, goethite (aFeOOH) have been described. It was concluded that this transformation consists of a dissolution of the lepidocrocite, a nucleation of goethite from the resultant Fe in solution and the crystalline growth of these nuclei. Any one of these three steps can be rate determining, depending on the conditions under which the transformation is being conducted.Since lepidocrocite, although less stable than goethite, exists in soils and sediments for long periods of time it is thought that soil constituents might be capable of retarding or even inhibiting the transformation. In this connection the observation of Hiller (1966) is interesting that the transformation of lepidocricite to goethite "can be completely inhibited by traces of silicate, aluminate and stannate". In our first paper (Schwertmann and Taylor, 1972) a similar observation has been mentioned. The following experiments were conducted to elucidate the influence of silicate on the various phases of the transformation.

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Section: Methodsmentioning

confidence: 99%

The Influence of Silicate on the Transformation of Lepidocrocite to Goethite

Schwertmann¹,

Rm²

1972

Clays and clay miner.

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“…Silicate at 30 mg L -1 (as SiO2) did not interfere with the determination of As by the proposed method. In the case of germanium, the requisite concentration of molybdenum for color development 23 is six times higher than that employed in this study. There are several reports staying the concentration level of germanium in ground water samples was 10 ng L -1 to 10 μg L -1 .…”

Section: Interferences From Other Ionsmentioning

confidence: 69%

Molybdenum Blue Spectrophotometry for Trace Arsenic in Ground Water Using a Soluble Membrane Filter and Calcium Carbonate Column

et al. 2013

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An improved molybdenum blue spectrophotometry using a soluble membrane filter and CaCO3-column was proposed for determining arsenic in drinking water supplied from ground water in the presence of phosphate. A 100 mL sample solution containing 0.5 -10 μg arsenic was passed through a CaCO3-column to remove phosphate, arsenate (As(V)). Arsenite (As(III)) which was not retained on the column was oxidized to As(V). As(V) was converted into a heteropolymolybdenum blue anion. The blue anion was collected on a membrane filter as an ion-associate with n-dodecyltrimethylammonium ion by filtration. The filter was dissolved in 2 mL of 2-methoxyethanol. The absorbance of the solution was measured at 810 nm against a reagent blank. Total inorganic arsenic was determined by reducing As(V) to As(III) before the column treatment. The RSDs for 10 μg L -1 of As(III) and As(V) were 2.9%. Phosphate 0.2 mg L -1 (as P) and iron 0.1 mg L -1 did not interfere with the determination of 10 μg L -1 arsenic. The proposed method was successfully applied to ground waters.

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“…The concentrations of Ca 2+ and K + were determined by flame emission spectrophotometry; of Mg 2+ by atomic absorption spectrophotometry in the presence of Sr 2 + (4000 ppm) which prevented interferences by other cations in solution. The concentration of Si(OH)4 was determined colorimetrically by the molybdosilicate method of Boltz and Mellon (1947).…”

Section: Methodsmentioning

confidence: 99%

Cation and Silica Relationships of Mica Weathering to Vermiculite in Calcareous Harps Soil

Henderson

Doner

Weaver

et al. 1976

Clays and clay miner.

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Abstrac~A steady state reaction of apparent equilibrium of K mica + Ca z+ ~ Ca vermiculite + K § was indicated by prolonged dissolution extractions from Blount soil clay (from northern Indiana) abundant in dioctahedral mica and vermiculite, with log Keq = 2.92 for the reaction when extrapolated to infinite time. From this and published free energies of formation of mica and kaolinite, a mineral phase stability diagram depicting the phase joins of Ca vermiculite, muscovite, and kaolinite was constructed with the solute activity functions pH-pK +, 2pH~Ca z +, and pSi(OH)4. These solute functions for 14-day reactions of calcareous (and dolomitic), poorly drained Harps soil (from central Iowa) fell near the calcite-dolomite-COz-H20 phase join, suggesting equilibrium. These functions for Harps soil and the control minerals muscovite, biotite, and (or) vermiculite plus calcite were plotted on the mica-vermiculite stability diagram for various COz partial pressures. The points fell on the vermiculite-stable side of the mica-vermiculite plane at CO2 partial pressures of 0.15 and 0.20 atm (similar to soil air that would exist under frozen soil during winter and early spring; 2pH-pCa z+ -~ 10.3). They fell on the muscovite-stable side of the muscovite-vermiculite plane at CO2 partial pressures of 0.0001 and 0.001 atm (similar to soil air under natural summer conditions; 2pH-pCa z+, 13.6 and 12.6, respectively) and therefore K § (and 137Cs+ in rainfall) would be expected to be fixed.The 2pH-pMg 2+ values determined for Harps soil at the various COz partial pressures plotted either in the Mg montmorillonite stability field or on the Mg-montmorillonite-kaolinite phase join, in concordance with the abundance of montmorillonite and some kaolinite in the medium and fine clay fractions. The solute values for the nearby Clarion soil (upland, noncalcareous) plotted on the montmorillonite kaolinite join, or with higher CO2 partial pressure, in the kaolinite stability area. The Gibbs free energy of formation (AG~) for a dioctahedral Ca vermiculite of -1303.7 kcal per 010 was determined from the Keq. The solute functions for the Blount soil showed kaolinite to be the thermodynamically stable phase with respect to dioctahedral mica and (or) vermiculite. The 14-day solute values for the Harps and upland Clarion soils were also on the kaolinite stability side of the kaolinite-vermiculite join. The kinetics of kaolinite formation in the upper midwestern U.S.A. are apparently slow on a scale of ~ 104 years.

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Determination of Phosphorus, Germanium, Silicon, and Arsenic

Cited by 205 publications

References 27 publications

The Influence of Silicate on the Transformation of Lepidocrocite to Goethite

The Influence of Silicate on the Transformation of Lepidocrocite to Goethite

Molybdenum Blue Spectrophotometry for Trace Arsenic in Ground Water Using a Soluble Membrane Filter and Calcium Carbonate Column

Cation and Silica Relationships of Mica Weathering to Vermiculite in Calcareous Harps Soil

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